Field of the Invention
In sheet-fed printing presses, depending on its configuration, a sheet leaving a processing station must be supported at a variable number of points on its concave side during a deflection of the sheets that is done with corresponding compulsory guidance of the leading edge of the sheets in the processing direction. The concave side is often a freshly printed side of the sheets, so that the support must be accomplished without smearing. To that end, depending on the conditions of a printing job, sheet guide drums are used, which by skeleton-like sheet supports, such as a rowel assembly, have only an imaginary drum jacket face in the form of an envelope surface enclosing the sheet supports, or sheet guide drums that have a real drum jacket face. If the proper type of sheet guide drums, of the different types discussed thus far, are to be used, it may be necessary, along with the change from one printing job to the next, also to replace the sheet guide drums of one type with another. However, this often entails considerable assembly work, quite aside from the fact that the real drum jacket face, made as a cast part, for instance, can have a considerable weight. The assembly work may not be limited to merely replacing the sheet guide drum. To enable the installation and removal of the sheet guide drum, many parts of the printing press located around it, such as blowers, powder applicators or others, first have to be removed and then once the suitable sheet guide drum has been installed they have to be reinstalled as well. This leads to relatively long down times of the printing press upon a change of printing job and thus represents a cost factor that is deleterious to the economy of the printing press.